A printed board having a pattern fuse, which is a part of wiring patterns formed in the printed board, is known in the art, for example, as disclosed in Japanese Patent Publication No. 2007-311467.
The pattern fuse is generally so formed as to be narrower than a remaining part of the wiring patterns. Therefore, for example, when a short-circuit occurs in an inside of an electronic device or an electronic part and thereby excess current flows, the pattern fuse is melted down due to heat generation in order that an electric pathway is cut off.
In a case of the pattern fuse, it is necessary to individually design the pattern fuses when the pattern fuses are used for different types of electronic parts or when the pattern fuses are used to the same type of the electronic part but ratings of the electronic parts are different from each other. As a result, it is difficult to commonalize or standardize the printed boards for different types of electronic control units. In other words, it is difficult to commonalize the printed boards and to simply change the electronic parts to be mounted to the printed board in order to use the same type of the printed board for the different types of the electronic control units (variation products).
In addition, it is difficult to make a size of the printed board as well as the electronic control unit smaller, because the pattern fuse (or pattern fuses) is formed in the printed board as a part of the wiring patterns.
In addition, the heat generated at the pattern fuse due to the excess current directly goes away to an insulating board of the printed board neighboring to the pattern fuse or the heat generated at the pattern fuse may indirectly go away to the insulating board via the wiring pattern connected to the pattern fuse. Since the heat of the pattern fuse goes away to the insulating board as above, it is a problem that it may take a longer time from short-circuit in the electronic part to melt-down of the pattern fuse. In other words, it is not possible to quickly cut off the pattern fuse with high response. In addition, since response characteristics vary, it is not possible to assure accuracy of performance for cutting off the pattern fuse.